A Storage Area Network (SAN) attaches remote computer storage devices or drives such as a disk array, tape library or one or more optical storage drives to servers such that the storage devices appear as locally attached in a client-server relationship. Many Storage Area Networks use a SCSI protocol for communicating between servers and the disk drives, while employing a low-level protocol and mapping layer, for example, a Fibre Channel (FC) over an Ethernet connection.
For example, in the television broadcast industry, video servers or other data servers are often connected to fibre channel storage devices through fibre channel switches. An example of such a video system is manufactured by Harris Corporation of Melbourne, Fla. as the Nexio™ line of network video servers, switches and storage devices. The fibre channel can run on both twisted pair copper wire and fibre-optic cables with a physical connection that could be optical or non-optical. The Fibre Channel Protocol (FCP) is typically an interface protocol of SCSI on the fibre channel. The different fibre channel topologies can include point-to-point topology in which the storage devices are connected back-to-back, an arbitrated loop topology in which devices are in a loop or ring, and a switched fabric topology in which the devices or loop devices are connected to fibre channel switches, similar to an Ethernet implementation with the switches managing the state of the fabric to provide optimized connections. Usually fibre channel switches can be formed as directors that offer a high port count in a modular slot-based chassis or a smaller, fixed configuration.
Storage Area Networks that use video servers in the television broadcast industry require real time data delivery and typically support guaranteed delivery and SAN coherency in content server systems. The high data rates are typical for a streaming server, for example, 1/60th of a second, quality of service, as video frames. Small disruptions can create editing and server function problems.
Because of the high data rates required to support multiple broadcast quality video streams, the video and other server systems were traditionally built with the compressors, decompressors and signal input/output devices physically located in a computer server frame to take advantage of high speed, low latency data transfer buses. This server frame typically used a direct attached, block based storage to obtain the required data rates and a SAN for the purpose of sharing that storage with other server frames. One technique used in the television broadcast industry to achieve redundancy and reliability in this type of direct attached storage was to use off-the-shelf fibre channel technology with redundant fibre channel host ports on the server and connected to redundant fibre channel target ports on the drives. As the drive throughput and fibre channel physical layer throughput rose, larger populations of servers could be supported. Eventually, however, server populations rise to the point where further direct attachment connections are no longer possible because of limitations in the number of fibre channel log-ins permitted by the drives even though the drives are capable of delivering more data than can be used by the maximum population of content stream support components physically located in the direct attach servers.
Because of this limitation, any increase in the number of data streams required the separation of the direct storage attached server from the data stream support components using the standard client-server architecture. The full dual path redundancy of the integrated solution should be maintained because of the mission critical nature of the content or data streams within the television broadcast environment. For this reason, some systems maintained their redundant connections through dual Ethernet connections to the data or video servers while load balancing across Ethernet connections. Other server systems abandoned load balancing and configured an additional server, while others used redundant Ethernet connections from the client to the server and load balanced the Ethernet connections from the client to the server such that redundant data servers are constantly in use because of the load balancing. These systems provided adequate results, but greater enhancements to the efficiency of the Storage Area Network are desirable to allow load balanced streaming data and redundancy.